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Publication Abstract from PubMed

NAD(+)-dependent DNA ligase (LigA) is the essential replicative ligase in bacteria and differs from ATP-dependent counterparts like the human DNA ligase I (HligI) in several aspects. LigA uses NAD(+) as the co-factor while the latter uses ATP. Further, the LigA carries out enzymatic activity with a single divalent metal ion in the active site while ATP-dependent ligases use two metal ions. Instead of the second metal ion, LigA have a unique NMN binding subdomain that facilitates the orientation of the beta-phosphate and NMN leaving group. LigA are therefore attractive targets for new anti-bacterial therapeutic development. Others and our group have earlier identified several LigA inhibitors that mainly bind to AMP binding site of LigA. However, no inhibitor is known to bind to the unique NMN binding subdomain. We initiated a fragment inhibitor discovery campaign against the M. tuberculosis LigA based on our co-crystal structure of adenylation domain with AMP and NMN. The study identified two fragments, 4-(4-fluorophenyl)-4,5,6,7-tetrahydro-3H imidazo[4,5-c] pyridine and N-(4-methylbenzyl)-1H-pyrrole-2-carboxamide, that bind to the NMN site. The fragments inhibit LigA with IC50 of 16.9 and 28.7 microM respectively and exhibit MIC of ~20 and 60 microg/ml against a temperature sensitive E. coli GR501 ligA(ts) strain, rescued by MtbLigA. Co-crystal structures of the fragments with the adenylation domain of LigA show that they mimic the interactions of NMN. Overall, our results suggest that the NMN binding-site is a druggable target site for developing anti-LigA therapeutic strategies.

Structure based identification of first-in-class fragment inhibitors that target the NMN pocket of M. tuberculosis NAD(+)-dependent DNA ligase A.,Shukla A, Afsar M, Kumar N, Kumar S, Ramachandran R J Struct Biol. 2021 Mar;213(1):107655. doi: 10.1016/j.jsb.2020.107655. Epub 2020 , Nov 13. PMID:33197566^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.